Local time distribution of net field‐aligned currents derived from high‐altitude satellite data

Abstract

[1] In order to explain features of geomagnetic disturbances observed at low and middle latitudes such as the dawn-dusk asymmetry in the north-south component, an antisunward current system has been proposed. The antisunward current system consists of net downward field-aligned currents on the dayside, antisunward auroral electrojet currents, and net upward field-aligned currents on the nightside. However, the net field-aligned currents consisting in this current system have not been established by spacecraft observations yet. In order to discuss whether this antisunward current system actually exists or not and whether this current system actually causes the features of geomagnetic disturbances at low and middle latitudes or not, we statistically investigated the global structure of the geomagnetic disturbances generated by the field-aligned currents in the inner magnetosphere by using the magnetic field data obtained by the DE-1 satellite. On the basis of the results, local time distribution of the net field-aligned currents was estimated. Net downward currents are found in the prenoon sector, and net upward currents are found in the premidnight sector. In the postnoon and the postmidnight sector, net field-aligned currents are rather small on an average. The net downward field-aligned currents in the prenoon would feed some portions of the auroral electrojets, and the portions would flow from the prenoon to the premidnight to connect with the net upward field-aligned currents in the premidnight. These results are consistent with ground geomagnetic observations in the auroral region. In addition, we proposed a possible current system, which consistently explains our results and many other observations. It was also confirmed that the current system can actually cause the features of geomagnetic disturbances on the ground.

Space Technology 5 observations of the imbalance of regions 1 and 2 field‐aligned currents and its implication to the cross‐polar cap Pedersen currents

“…Most of the current closure takes place via local Pedersen currents within the auroral zone flowing between the upward and downward FACs. However, observations show that there is generally an imbalance in total currents between the pair of opposite flowing R1 and R2 FACs in either dawnside or duskside, i.e., the total current flowing in R1 FCAs is more than that in R2 FACs [ Iijima and Potemra , 1976; Sugiura and Potemra , 1976; Fujii et al , 1981, 1994; Stauning and Primdahl , 2000; Fujii and Iijima , 1987; Nakano et al , 2002; Nakano and Iyemori , 2003; Christiansen et al , 2002]. Thus, there are net currents into (out of) the ionosphere due to the R1‐R2 imbalance in the dawnside (duskside) auroral region.…”

Storm‐time field‐aligned currents on the nightside inferred from ground‐based magnetic data at midlatitudes: Relationships with the interplanetary magnetic field and substorms

“…On the other hand, an eastward/westward disturbance in the northern/southern hemisphere over the entire nightside is also common at midlatitudes (hereafter we will refer to eastward disturbances in the northern hemisphere and westward disturbances in the southern hemisphere as “positive” east‐west disturbances) [e.g., Iyemori , 1990; see also Yamashita et al , 2002]. These positive disturbances have been explained as a superposition of the effects of the Region 1 current system and those of the Region 2 current system by Nakano and Iyemori [2003].…”

The Shape of Strongly Disturbed Dayside Magnetopause

“…On the other hand, Nakano and Iyemori (2003) showed that during magnetic storms, the magnitude of region 2 FACs was comparable with region 1 currents in the postnoon and premidnight sectors and, thus, the net contribution of the region 1 and 2 FACs was small. This finding supports the experimental result conducted by Nagai (1982) who found that no appreciable variations in the dayside geosynchronous magnetic field are associated with the Birkeland currents during geomagnetic storms.…”